feature

Monolithic 700V sense FET power switch Precisely fixed operating frequency (134kHz) Advanced burst mode operation consumes less than 0.1W at 265V AC and no load ( FSD210 only) Internal start switch and soft start Undervoltage lockout with hysteresis (uvlo ) Pulse-by-Pulse Current Limit Overload Protection (OLP) Internal Thermal Shutdown (TSD) Auto-Restart Mode EMI Frequency Modulation FSD200 does not require auxiliary bias winding

application

Chargers and adapters for cell phones, PDAs and MP3s Auxiliary power supply for white goods, PCs, C-TVs and monitors

illustrate

The fsd200 and fsd210 are integrated pulse width modulators (pwm) and sensing fets designed for high performance offline switch mode power supplies (SMPS) with minimal external components. Both devices are monolithic high voltage power switching regulators that combine an LDMOS sensing FET and a voltage mode pwm control block. Features of the integrated pwm controller include: a fixed oscillator with frequency modulation to reduce EMI, undervoltage lockout (uvlo) protection, leading edge blanking (LEB), optimized gate switch driver, thermal shutdown protection (TSD) ), temperature compensation precision current source for loop compensation and fault protection circuits. Compared to discrete mosfet and controller or rcc switching converter solutions, the fsd200 and fsd210 reduce total component count, design size, and weight while increasing efficiency, productivity, and system reliability. The FSD200 eliminates the need for miniaturization of the auxiliary bias winding. Increase the cost of electricity. Both devices are a basic platform well suited for cost-effective design of flyback converters.

Function description

1. Startup: During startup, the internal high voltage current source provides internal bias and charges the external VCC capacitor as shown in Figure 7. In this case fsd210, when vcc reaches 8.7v, the device starts switching the internal high voltage current source is disabled (see diagram). If vcc is not lower than 6.7V. For the FSD210, the post-start bias is provided from the auxiliary transformer winding. In the case of the FSD200, VCC is supplied by an external high voltage supply and VCC is passed through an internal high voltage regulator (HVREG), thus eliminating the need for an auxiliary winding (see figure).

The calculation of the VCC capacitor is an important step in the design of the MPC506AU for the FSD200/210. At the initial startup of the FSD200/210, the standby maximum current is 100uA, supplying power to the UVLO and VREF blocks. The charging current (I) of the VCC capacitor is equal to ISTR-100uA. VCC then supplies VCC current to the device only when the bias winding reaches the UVLO startup voltage. When the bias winding voltage is insufficient, the VCC level drops to the UVLO stop voltage. At this time, VCC oscillates. To prevent it is recommended to adjust the size of the VCC capacitor between 10uf and 47uf. 2. Feedback control: fsd200/210 are both voltage mode devices as shown in Figure 8. Usually H11A817 optocoupler and KA431 voltage reference (or FOD2741 integrated optocoupler and voltage reference) are used to implement isolated secondary feedback network. This feedback voltage and the internally generated sawtooth wave directly control the duty cycle. When the KA431 reference pin voltage exceeds the internal reference voltage of 2.5V, the optocoupler LED current increases the pull-down feedback voltage and reduces the duty cycle. when the input voltage increases or the output load decreases.

3. Leading edge blanking (Leb): At the moment when the internal sensing FET is turned on, there is usually a large current spike of the induced current transformer caused by the primary side. Capacitor and secondary side rectifier diode reverse recovery. Exceeding the pulse current limit may cause premature termination of switching pulses. To counteract this effect, fps uses a leading

Edge Blanking (LEB) circuit. This circuit inhibits the current comparator FET from turning on for a short time after overvoltage sensing.

4. Protection circuit: FSD200/210 has two self-protection functions, overload protection (OLP) and thermal shutdown (TSD). Because these protection circuits are integrated into the integrated circuit, there are no external components, and the system improves reliability without increasing cost. If these thresholds are triggered, the fps starts an automatic restart loop. Once a fault occurs, the switch is terminated and the inductive FET remains off. This results in VCC. When VCC reaches the UVLO stop voltage (6.7V:fsd210, 6V:fsd200), the protection is reset and the internal high voltage current source charges the VCC capacitor. When the vcc reaches the uvlo startup voltage (8.7V:fsd210, 7V:fsd200), the device tries to resume normal operation. Startup succeeds if the fault condition no longer exists. If it still exists, the cycle is repeating (see picture).

4.1 Overload Protection (OLP): Overload Protection When the load current is due to an abnormal situation If this happens, the protection circuit should be triggered to protect the smps. It is possible that under normal operating conditions, short-term load transients may occur. In order to avoid false shutdown, the overload protection circuit is designed as a delay trigger. The device can thus distinguish between transient overloads and true fault conditions. The maximum input power is limited. Use the pulse-by-pulse current limit feature. If the load tries to pull harder, the output voltage will drop to the set value. This reduces the optocoupler LED current and thus the phototransistor current. Therefore, the 250ua current source will charge the feedback pin capacitor cfb and the feedback voltage vfb will increase. The input to the feedback comparator is limited to 3VV. Once VFB reaches 3V, the device switches to its maximum power supply, the 250uA current source is blocked, and the 5uA source continues to charge the CFB. Once VFB reaches 4V, switching stops and overload protection is triggered. The resulting shutdown delay time was set by the time required to charge the CFB with 5uA from 3v to 4vw as shown. 4.2 Thermal Shutdown (TSD): The sensing FET and the control IC make it easier for the control IC to detect the temperature of the sensing FET. Thermal shutdown is activated when the temperature exceeds approximately 145°C.

5. Soft start: FSD200/210 has an internal soft start circuit that gradually increases the current through the induction FET as shown in the figure. The fsd200 soft-start time is 3ms/210.

6. Burst operation: To minimize power consumption in standby mode, fsd200/210 implements burst mode function (see figure). As the load decreases, the feedback voltage decreases. As shown in the picture, the device automatically enters burst mode when the feedback voltage is lower than vburl (0.58v). The rate at which switching stops and the output voltage begins to drop depends on the standby current load. This causes the feedback voltage to go up. Once through vburh (0.64v), the switch kicks in again. The feedback voltage drops and the process repeats. Burst Mode operation alternately enables and disables power-sensing FETs, reducing switching losses

7. Frequency modulation: EMI reduction can be achieved by modulating the switching frequency of the switching power supply. Frequency modulation can spread the energy over a wider frequency range. The amount of EMI reduction is directly related to the modulation level (fmod) and the modulation rate. As shown, the frequency changes from 130kHz to 138kHz in 4ms for the FSD200/FSD210. Frequency modulation allows the use of cost-effective inductors in place of AC input mode chokes to meet global EMI limits.

feature

High Efficiency (Universal Input >67%) Low Zero-Load Power Consumption (<100MW at 240Vac) with FSD210 Small Number of Components Improves System Reliability Through Various Protection Functions Internal Soft Start (3ms) Low EMI Frequency Modulation Key Design Description Constant Voltage (cv) mode control is achieved through resistors r8, r9, r10 and r11, shunt regulator u2, feedback capacitor, C9 and optocoupler, U3. Constant current (CC) mode control adopts resistors R8, R9, R15, R16, R17 and R19, NPN transistor, Q1 and NTC, TH1. When the voltage between current sense resistors r15, r16 and r17 is 0.7v, the npn transistor turns on, and the current through the optocoupler LED increases. This reduces the feedback voltage and duty cycle. Therefore, the output voltage is reduced and the output current is regulated. NTC (Negative Thermal Coefficient) is used to compensate the temperature characteristics of transistor Q1.